Optimizing a sequence of processes for manufacturing of product units

ABSTRACT

A method for optimizing a sequence of processes for manufacturing of product units, includes: associating measurement results of performance parameters (e.g., fingerprints) with the recorded process characteristics (e.g., context); obtaining a characteristic (e.g., context) of a previous process (e.g. deposition) in the sequence already performed on a product unit; obtaining a characteristic (e.g., context) of a subsequent process (e.g., exposure) in the sequence to be performed on the product unit; determining a predicted performance parameter (e.g., fingerprint) of the product unit associated with the sequence of previous and subsequent processes by using the obtained characteristics to retrieve measurement results of the performance parameters (e.g., fingerprints) corresponding to the recorded characteristics; and determining corrections to be applied to future processes (e.g. exposure, etch) in the sequence to be performed on the product unit, based on the determined predicted performance parameter.

This application is a continuation of U.S. patent application Ser. No.16/495,119 which was filed on Sep. 18, 2019, now allowed, which is theU.S. national phase entry of PCT Patent Application No.PCT/EP2018/057961 which was filed on Mar. 28, 2018, which claims thebenefit of priority of European Patent Application No. 17168734.6 whichwas filed on Apr. 28, 2017, each of the foregoing applications isincorporated herein in its entirety by reference.

FIELD

The present description relates to a method of optimizing a sequence ofprocesses for manufacturing of product units, usable, for example, inthe manufacturing of semiconductor device wafers by lithographictechniques. The present description also relates to associated computerprograms and computer program products, and apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,including part of, one, or several dies) on a substrate (e.g., a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. These target portions arecommonly referred to as “fields”. Wafers are processed in batches orlots through various apparatuses in the semiconductor fabricationfacility (fab). The integrated circuit is built up layer by layer with alithographic step performed by a lithographic apparatus at each layerand other fab processes being performed in between lithographic steps.

Before the imaging step, various chemical and/or physical processingsteps are used to form and prepare the layer for patterning. After theimaging step defines the pattern, further chemical and/or physicalprocessing steps work through the pattern to create functional featuresof the integrated circuit. The imaging and processing steps are repeatedin a multi-layer process to build integrated circuit.

SUMMARY

The accurate placement of patterns on the substrate is a chief challengefor reducing the size of circuit components and other products that maybe produced by lithography. In particular, the challenge of measuringaccurately the features on a substrate which have already been laid downis a critical step in being able to align successive layers of featuresin superposition accurately enough to produce working devices with ahigh yield. So-called overlay should, in general, be achieved within afew tens of nanometers in today's sub-micron semiconductor devices, downto a few nanometers in the most critical layers.

Consequently, modern lithography apparatuses involve extensivemeasurement or ‘mapping’ operations prior to the step of actuallyexposing or otherwise patterning the substrate at a target location.So-called advanced alignment models have been and continue to bedeveloped to model and correct more accurately non-linear distortions ofthe wafer ‘grid’ that are caused by processing steps and/or by thelithographic apparatus itself. Not all distortions are correctableduring exposure, however, and it remains important to trace andeliminate as many causes of such distortions as possible.

Modern multi-layer lithographic processes and products are so complexthat issues due to processing are difficult to trace back to the rootcause. Monitoring of wafer integrity and design of an appropriatecorrection strategy is therefore a time-consuming and laboriousexercise.

PCT Patent Application Publication No. WO 2015049087, which isincorporated by reference herein in its entirety, discloses a method ofobtaining diagnostic information relating to an industrial process.Alignment data or other measurements are made at stages during theperformance of the lithographic process to obtain object datarepresenting positional deviation or other parameters measured at pointsspatially distributed across each wafer. Overlay and alignment residualstypically show patterns across the wafer, known as fingerprints. Thisobject data is used to obtain diagnostic information by performing amultivariate analysis to decompose the set of vectors representing thewafers in multidimensional space into one or more component vectors.Diagnostic information about the industrial process is extracted usingthe component vectors. The performance of the industrial process forsubsequent wafers can be controlled based on the extracted diagnosticinformation.

In semiconductor manufacture, the Critical Dimension (CD) performanceparameter fingerprint can be corrected using a simple control loop.Typically a feedback mechanism controls the average dose per wafer,using the scanner (a type of lithographic apparatus) as an actuator.Similarly, for the overlay performance parameter overlay, fingerprintsinduced by processing tools can be corrected by adjusting scanneractuators.

However, a drawback with such approaches is that the granularity ofcorrections is still limited. Each wafer from a lot gets the samecorrection, i.e. there are lot level corrections. What is more, only themost suitable one of available actuators (e.g. scanner or etcher) isused to correct for disturbance fingerprints.

Wafer-to-wafer variations exist within a lot and optimization of thewhole litho process (CMP/deposit/coat/expose/develop/etch/deposit/ . . ., etc.) is not optimal in view of the available sensor and metrologydata and degrees of freedom of actuators for making corrections.

Accordingly, there is provided a way to optimize a sequence ofprocesses. It may be used, for example, in the manufacture of devices bylithographic techniques to reduce the adverse effects of fingerprintssuch as deposition thickness variation and etcher fingerprint onafter-etch CD, hence increasing yield, while avoiding or at leastmitigating one or more of the associated problems mentioned above.

In an aspect, there is provided a method for optimizing a sequence ofprocesses for manufacturing of product units, the method comprising:

(a) obtaining a characteristic of a previous process in the sequencealready performed on a product unit;

(b) obtaining a characteristic of a subsequent process in the sequenceto be performed on the product unit;

(c) determining, using the obtained characteristics, a predictedperformance parameter of the product unit associated with the sequenceof previous and subsequent processes; and

(d) determining a first correction to a first future process in thesequence to be performed on the product unit, based on the determinedpredicted performance parameter.

The step (c) of determining the predicted performance parameter maycomprise the steps:

(c1) obtaining recorded characteristics of processes in the sequenceperformed on a plurality of product units;

(c2) obtaining measurement results of performance parameters for eachproduct unit out of the plurality of product units;

(c3) associating the measurement results of the performance parameterswith the respective recorded characteristics; and

(c4) determining a predicted performance parameter of the product unitassociated with the sequence of previous and subsequent processes byusing the obtained characteristics to retrieve measurement results ofthe performance parameters corresponding to the recordedcharacteristics.

In an aspect, there is provided a computer program comprising computerreadable instructions which, when run on suitable computer apparatus,cause the computer apparatus to perform a method as described herein.

In an aspect, there is provided a computer program product comprising acomputer program as described herein.

In an aspect, there is provided an apparatus specifically adapted tocarry out the steps of a method as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings in which:

FIG. 1 depicts a lithographic apparatus together with other toolsforming a production facility for semiconductor devices.

FIG. 2 depicts a high-level flow diagram of measurement results ofperformance parameters being associated with recorded characteristics ofa sequence of processes, in accordance with an embodiment of the presentinvention.

FIG. 3 depicts a high-level flow diagram of determining and applyingcorrections to two processes in the sequence of FIG. 2, in accordancewith an embodiment of the present invention.

FIG. 4 is a flowchart of a method in accordance with an embodiment ofthe present invention.

FIG. 5 illustrates computing apparatus useful in implementing themethods disclosed herein.

DETAILED DESCRIPTION

Before describing embodiments of the invention in detail, it isinstructive to present an example environment in which embodiments ofthe present invention may be implemented.

FIG. 1 at 100 shows a lithographic apparatus LA as part of an industrialfacility implementing a high-volume, lithographic manufacturing process.In the present example, the manufacturing process is adapted for themanufacture of for semiconductor products (integrated circuits) onsubstrates such as semiconductor wafers. The skilled person willappreciate that a wide variety of products can be manufactured byprocessing different types of substrates in variants of this process.The production of semiconductor products is used purely as an examplewhich has great commercial significance today.

Within the lithographic apparatus (or “litho tool” 100 for short), ameasurement station MEA is shown at 102 and an exposure station EXP isshown at 104. A control unit LACU is shown at 106. In this example, eachsubstrate visits the measurement station and the exposure station tohave a pattern applied. In an optical lithographic apparatus, forexample, a projection system is used to transfer a product pattern froma patterning device MA onto the substrate using conditioned radiationand a projection system. This is done by forming an image of the patternin a layer of radiation-sensitive resist material.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. The patterning MA device maybe a mask or reticle, which imparts a pattern to a radiation beamtransmitted or reflected by the patterning device. Well-known modes ofoperation include a stepping mode and a scanning mode. As is well known,the projection system may cooperate with support and positioning systemsfor the substrate and the patterning device in a variety of ways toapply a desired pattern to many target portions across a substrate.Programmable patterning devices may be used instead of reticles having afixed pattern. The radiation for example may include electromagneticradiation in the deep ultraviolet (DUV) or extreme ultraviolet (EUV)wavebands. The present disclosure is also applicable to other types oflithographic process, for example imprint lithography and direct writinglithography, for example by electron beam.

The lithographic apparatus control unit LACU controls all the movementsand measurements of various actuators and sensors, causing the apparatusto receive substrates W and reticles MA and to implement the patterningoperations. LACU also includes signal processing and computing capacityto implement desired calculations relevant to the operation of theapparatus. In practice, control unit LACU will be realized as a systemof many sub-units, each handling the real-time data acquisition,processing and control of a subsystem or component within the apparatus.

Before the pattern is applied to a substrate at the exposure stationEXP, the substrate is processed in at the measurement station MEA sothat various preparatory steps may be carried out. The preparatory stepsmay include mapping the surface height of the substrate using a levelsensor and measuring the position of alignment marks on the substrateusing an alignment sensor. The alignment marks are arranged nominally ina regular grid pattern. However, due to inaccuracies in creating themarks and also due to deformations of the substrate that occurthroughout its processing, the marks deviate from the ideal grid.Consequently, in addition to measuring position and orientation of thesubstrate, the alignment sensor in practice must measure in detail thepositions of many marks across the substrate area, if the apparatus isto print product features at the correct locations with very highaccuracy.

The lithographic apparatus LA may be of a so-called dual stage typewhich has two substrate tables, each with a positioning systemcontrolled by the control unit LACU. While one substrate on onesubstrate table is being exposed at the exposure station EXP, anothersubstrate can be loaded onto the other substrate table at themeasurement station MEA so that various preparatory steps may be carriedout. The measurement of alignment marks is therefore very time-consumingand the provision of two substrate tables enables a substantial increasein the throughput of the apparatus. If the position sensor IF is notcapable of measuring the position of the substrate table while it is atthe measurement station as well as at the exposure station, a secondposition sensor may be provided to enable the positions of the substratetable to be tracked at both stations. When lithographic apparatus LA isof a so-called dual stage type which has two substrate tables, theexposure station and the measurement station may be distinct locationsbetween which the substrate tables can be exchanged. This is only onepossible arrangement, however, and the measurement station and exposurestation need not be so distinct. For example, it is known to have asingle substrate table, to which a measurement stage is temporarilycoupled during the pre-exposure measuring phase. The present disclosureis not limited to either type of system.

Within the production facility, apparatus 100 forms part of a “lithocell” or “litho cluster” that contains also a coating apparatus 108(COA) for applying photosensitive resist and other coatings tosubstrates W for patterning by the apparatus 100. At an output side ofapparatus 100, a baking apparatus 110 and developing apparatus 112 areprovided for developing the exposed pattern into a physical resistpattern. Between all of these apparatuses, substrate handling systemstake care of supporting the substrates and transferring them from onepiece of apparatus to the next. These apparatuses, which are oftencollectively referred to as the “track”, are under the control of atrack control unit which is itself controlled by a supervisory controlsystem SCS, which also controls the lithographic apparatus vialithographic apparatus control unit LACU. Thus, the differentapparatuses can be operated to maximize throughput and processingefficiency. Supervisory control system SCS receives recipe information Rwhich provides in great detail a definition of the steps to be performedto create each patterned substrate.

Once the pattern has been applied and developed in the litho cell,patterned substrates 120 are transferred to other processing apparatusessuch as are illustrated at 122, 124, 126. A wide range of processingsteps is implemented by various apparatuses in a typical manufacturingfacility. For the sake of example, apparatus 122 in this embodiment isan etching station (ETC), and apparatus 124 performs a post-etch thermalannealing step (ANN). Further physical and/or chemical processing stepsare applied in further apparatuses, 126, etc. Numerous types ofoperation can be required to make a real device, such as deposition ofmaterial (DEP), modification of surface material characteristics(oxidation, doping, ion implantation etc.), chemical-mechanicalpolishing (CMP), and so forth. The apparatus 126 may, in practice,represent a series of different processing steps performed in one ormore apparatuses.

As is well known, the manufacture of semiconductor devices involves manyrepetitions of such processing, to build up device structures withappropriate materials and patterns, layer-by-layer on the substrate.Accordingly, substrates 130 arriving at the litho cluster may be newlyprepared substrates, or they may be substrates that have been processedpreviously in this cluster or in another apparatus entirely. Similarly,depending on the required processing, substrates 132 on leavingapparatus 126 may be returned for a subsequent patterning operation inthe same litho cluster, they may be destined for patterning operationsin a different cluster, or they may be finished products to be sent fordicing and packaging.

Each layer of the product structure requires a different set of processsteps, and the apparatuses 126 used at each layer may be completelydifferent in type. Further, even where the processing steps to beapplied by the apparatus 126 are nominally the same, in a largefacility, there may be several supposedly identical machines working inparallel to perform the step 126 on different substrates. Smalldifferences in set-up or faults between these machines can mean thatthey influence different substrates in different ways. Even steps thatare relatively common to each layer, such as etching (apparatus 122) maybe implemented by several etching apparatuses that are nominallyidentical but working in parallel to maximize throughput. In practice,moreover, different layers require different etch processes, for examplechemical etches, plasma etches, according to the details of the materialto be etched, and special requirements such as, for example, anisotropicetching.

The previous and/or subsequent processes may be performed in otherlithography apparatuses, as just mentioned, and may even be performed indifferent types of lithography apparatus. For example, some layers inthe device manufacturing process which are very demanding in parameterssuch as resolution and overlay may be performed in a more advancedlithography tool than other layers that are less demanding. Thereforesome layers may be exposed in an immersion type lithography tool, whileothers are exposed in a ‘dry’ tool. Some layers may be exposed in a toolworking at DUV wavelengths, while others are exposed using EUVwavelength radiation.

In order that the substrates that are exposed by the lithographicapparatus are exposed correctly and consistently, it is desirable toinspect exposed substrates to measure properties such as overlay errorsbetween subsequent layers, line thicknesses, critical dimensions (CD),etc. Accordingly a manufacturing facility in which litho cell LC islocated also includes metrology system MET which receives some or all ofthe substrates W that have been processed in the litho cell. Metrologyresults are provided directly or indirectly to the supervisory controlsystem (SCS) 138. If errors are detected, adjustments may be made toexposures of subsequent substrates, especially if the metrology can bedone soon and fast enough that other substrates of the same batch arestill to be exposed. Also, already exposed substrates may be strippedand reworked to improve yield, or discarded, thereby avoiding performingfurther processing on substrates that are known to be faulty. In a casewhere only some target portions of a substrate are faulty, furtherexposures can be performed only on those target portions which are good.

Also shown in FIG. 1 is a metrology apparatus 140 (MET) which isprovided for making measurements of parameters of the products atdesired stages in the manufacturing process. A common example of ametrology apparatus in a modern lithographic production facility is ascatterometer, for example an angle-resolved scatterometer or aspectroscopic scatterometer, and it may be applied to measure propertiesof the developed substrates at 120 prior to etching in the apparatus122. Using metrology apparatus 140, it may be determined, for example,that important performance parameters such as overlay or criticaldimension (CD) do not meet specified accuracy requirements in thedeveloped resist. Prior to the etching step, the opportunity exists tostrip the developed resist and reprocess the substrates 120 through thelitho cluster. As is also well known, the metrology results 142 from theapparatus 140 can be used to maintain accurate performance of thepatterning operations in the litho cluster, by supervisory controlsystem SCS and/or control unit LACU 106 making small adjustments 166over time, thereby minimizing the risk of products being madeout-of-specification, and requiring re-work. Of course, metrologyapparatus 140 and/or other metrology apparatuses (not shown) can beapplied to measure properties of the processed substrates 132, 134, andincoming substrates 130.

Conventionally, semiconductor manufacturers make a process thread andtry and keep the wafers in that process thread. A thread is the sequenceof specific tools that a wafer is processed in as it progresses througha sequence of processes in the fab. Then all wafers get a constantfingerprint and a per-lot correction can be made to control thefingerprint. In order to get the best throughput it is best not todedicate any of the process flows. In practice it is not possible toprocess every wafer with the same tools. Especially not if we considereach chamber in the etch tool as a separate tool, because wafers in alot can be split across, for example, six etch chambers. Each chambermay cause a slightly different fingerprint. In for example semiconductormemory device processing, where throughput is very important, differentwafers from within a lot can be processed through different etch toolsas well as through different chambers of one etch tool.

Embodiments of the present invention decouple the contributions ofindividual processes to a performance parameter (e.g. after-etch overlayand CD fingerprint). This is be done by recording performance parameterresults (fingerprints) obtained for many different threads. Theperformance parameter results (fingerprints) are generated within a timescale less than stability processes. The method may use statisticalmethods to retrieve a context to performance model. For example, thethread: coat tool #1+scanner tool #3+etch tool #1+deposit tool #12 isused by a CD uniformity optimization application to retrieve theperformance model CD(1,3,1,12) to predict a fingerprint.

When there is a wide variation in context (e.g. threads per wafer) onecan relate performance measurements (overlay/CD fingerprints) tospecific context parameters (e.g. tool ID (#), tool parameters, etc.). Acontext-to-performance model is created which is able to derive from acertain context a predicted (after etch) performance of the lithographicprocess as a whole. The creation of such a model is described below withreference to FIG. 2.

Such a context-to-performance model is of great utility as it allowsprocess (e.g. scanner and etch) corrections on subsequent process steps(e.g. the next layers).

Once the model is created, it can be used to correct fingerprints onwafers in progress in the fab. Having recorded the previous thread of awafer and predicted the contribution of the processes including apost-expose process, it is possible to calculate an exposure correctiontaking into account the contribution to CD/overlay of a) the history ofsubstrate and b) future processing.

For example, with the context up to process N−1 known we can predictedoverlay fingerprint delta due to processes N+1, . . . we can thencorrect process N (exposure) based on the predicted overlay fingerprintdelta and anticipated correction applied to process N+M (etch).

The actuation that applies the corrections per process thus evolvesbased on the history of the wafer and future process characteristics.All corrections may be on a per wafer basis, minimizing wafer-to-wafervariations. Adopting this strategy, the full benefit of multi-toolcorrection potential can be obtained at a highly granular scale (perwafer, per group of wafers having similar contexts).

FIG. 2 depicts a high-level flow diagram of measurement results ofperformance parameters being associated with recorded characteristics ofa sequence of processes for manufacturing of product units. In thisexample, shown in FIGS. 2 and 3, the product units are wafers ofsemiconductor devices. The characteristics of the processes are contextdata. The context data represents one or more parameters of processingof product units, such as a tool identifier or measured processparameter. Also, in this example, the measurement results of performanceparameters are measured fingerprints. Thus the performance parametercomprises a fingerprint of variation across wafers of object datarepresenting one or more parameters measured across wafers.

With reference to FIG. 2, a sequence of processes 202 is performed onwafers. The processes include at 204, for example, chemical-mechanicalpolish (CMP), deposition (DEP), thermal anneal (ANN) and resist coat(COA). The processes also include: at 206, exposure (EXP) on a pluralityof scanner tools; at 208, etch (ETC) on a plurality of etch tools(including different etch chambers); and at 210 metrology (MET), such asafter-etch inspection (AEI) for CD and overlay measurement. Theseprocesses correspond to those shown in FIG. 1 having the same referencelabels (COA, EXP, ETC, and so on).

A setup application 212 obtains recorded characteristics of processes204 (e.g. CMP/DEP/ANN/COA), 206 (EXP) and 208 (ETC) in the sequence 202performed on many wafers. For example, deposition context is obtainedfrom processes 204, exposure context from process 206 and etch contextfrom process 208. Deposition fingerprints are used as an example for theapplication of an embodiment of the present invention because no filmthickness is available. The amorphous carbon layer that is deposited mayvary in thickness across wafers and from deposition chamber todeposition chamber. Measurement tools cannot distinguish betweenthickness and hardness which relates to the thin-film optical propertiesof refractive index (n) and extinction coefficient (k).

The setup application 212 obtains measurement results of performanceparameters for each wafer out of the many wafers for which the contexthas been recorded. For example, after-etch inspection CD (AEI CD) isobtained from a metrology tool 210.

The setup application 212 obtains the AEI CDs with the respectiverecorded context. For example, this is done by calculating deposition,scanner and etch fingerprints and storing the fingerprints per contextin one or more databases. Thus 214 is a database with CD fingerprint perCMP/DEP/ANN/COA context, 216 is a database with CD fingerprint perexposure context, and 218 is a database with etch chamber fingerprintper exposure context. Although depicted as three separate databases,other suitable storage schemes may be used, such as storing in onedatabase or in a matrix in a computer memory.

FIG. 3 depicts a high-level flow diagram of determining and applyingcorrections to two processes for manufacturing of wafers in the sequence202 of FIG. 2. The determining of the corrections is based oncharacteristics of both a previous process 304 performed on wafers and afuture process 306, 308 to be performed.

A CD uniformity (CDU) optimization application 320 obtains acharacteristic (e.g. deposition context) of a previous process 304 (e.g.DEP) in the sequence 302 already performed on a wafer.

CDU optimization application 320 obtains a characteristic (exposurecontext) of a subsequent process 306 (EXP) in the sequence 302 to beperformed on the wafer. In this example an etch optimization application334 also obtains a characteristic (etch context) of another subsequentprocess 308 (ETC) in the sequence 202 to be performed on the wafer. TheCDU optimization application 320 may obtain context of several exposureand etch tools that are available to be used, so that fingerprints maybe predicted (as described below) for several potential process threadsthat might be scheduled through a particular set of tools. Thecorrections can be determined for the potential process thread with theleast severe predicted fingerprints. Alternatively, differentcorrections can be determined for the different potential processthreads and the most practical or effective correction selected.

CDU optimization application 320 determines, using the obtainedcharacteristics, a predicted performance parameter (in this example afingerprint) of the wafer associated with the sequence of previous 304and subsequent 306, 308 processes. In this embodiment, this is done byusing the obtained context to retrieve measured fingerprintscorresponding to the recorded context. Then the retrieved measuredfingerprints are combined to produce a predicted fingerprint, given theprocesses already performed on the wafer and subsequent processes thatare to be performed in the future.

In this example, CDU optimization application 320 uses depositioncontext to query the database 214 (represented by the arrow going from320 to 214). In response to the query, the deposition fingerprint isretrieved from the database 214 (represented by the arrow going from 214back to 320).

CDU optimization application 320 uses exposure context to query thedatabase 216 (represented by the arrow going from 320 to 216). Inresponse to the query, the exposure fingerprint is retrieved from thedatabase 216 (represented by the arrow going from 216 back to 320).

Etch optimization application 334 uses etch context to query thedatabase 218 (represented by the arrow going from 334 to 218). Inresponse to the query, the exposure fingerprint is retrieved from thedatabase 218 (represented by the arrow going from 218 back to 334).

Although the CDU optimization application 320 and etch optimizationapplication 334 are described as separate applications, they may beparts of one application, or may themselves be split into severalsoftware applications or programs.

The CDU optimization application 320 determines a predicted fingerprint(i.e. a performance parameter) of the wafer associated with the sequence302 of previous 304 and subsequent 306, 308 processes. Application 320evaluates the deposition fingerprint 322 and the exposure fingerprint330. The predicted fingerprint is a linear combination 324 of thedeposition 322 and exposure 330 fingerprints. The predicted fingerprintis combined 326 with a dose sensitivity 332 and scanner dose correctionsare then calculated 328. In this way, CDU optimization application 320determines a first correction to a first future process 306 (EXP) in thesequence 302 to be performed on the wafer, based on the determinedpredicted fingerprint. The correction is applied to the exposure process306 when the wafer is subjected to that process, as represented by thearrow going from 320 to 306.

The etch optimization application 334 determines a predicted fingerprint(i.e. a performance parameter) of the wafer associated with the sequence302 of previous 304 and subsequent 306, 308 processes. Application 334evaluates the etch fingerprint 336. The predicted fingerprint is used tocalculate corrections 338 for the future etch process. In this way, etchoptimization application 334 determines a second correction to a secondfuture process 308 (ETC), subsequent to the first future process (EXP)in the sequence to be performed on the wafer, based on the determinedpredicted fingerprint. The correction is applied to the etch process 308when the wafer is subjected to that process, by transmitting an etchrecipe to the etch tool, as represented by the arrow going from 334 to308.

FIG. 4 is a flowchart of a method for optimizing a sequence of processesfor manufacturing of product units in accordance with an embodiment ofthe present invention.

With reference to FIG. 4, and also FIGS. 2 and 3, the method has thesteps:

402: Obtaining recorded context of processes 204 (e.g. CMP/DEP/ANN/COA),206 (EXP) and 208 (ETC) in the sequence 202 performed on many wafers.

404: Obtaining measured fingerprints (i.e. measurement results ofperformance parameters) for each wafer out of the many wafers, from ametrology tool 210.

406: Associating the measured fingerprints with the respective recordedcontext. Steps 402 to 406 are described above in relation to FIG. 2. Theresults are databases 214, 216, 218.

408: Obtaining the context of a previous process 304 (e.g. DEP) in thesequence already performed on a wafer.

410: Obtaining the context of one or more subsequent process 306, 308(EXP, ETC) in the sequence to be performed on the wafer.

412: Determining, using the obtained context, a predicted fingerprint ofthe wafer associated with the sequence of previous and subsequentprocesses. In this embodiment, this is done by using the obtainedcontext to retrieve measured fingerprints corresponding to the recordedcontext. This step may involve deriving a model from statisticalanalysis of fingerprints for a plurality of contexts of processes in thesequence.

414: Determining a first correction 328 to a future process 306 (EXP) inthe sequence 302 to be performed on the wafer, based on the determinedpredicted fingerprint.

416: Determining a second correction 338 to a second future process 308(ETC), which in this example is subsequent to the first future process306 (EXP), in the sequence 302 to be performed on the wafer, based onthe determined predicted fingerprint. The first correction 328 mayrelate to variation across a plurality of tools (e.g. average) of thepredicted fingerprint associated with the second future process 308(ETC) and the second correction 338 relates to variation of a specifictool (e.g. etch chamber) used in the second future process 308. Thuscorrection is based on optimally distributed corrections at anindividual tool level (here using the scanner and etcher). For example,the scanner may correct average etch fingerprint, while the etchercorrection keeps chamber-to-chamber variation close to zero.

418: Applying the determined first 328 and second 338 corrections toprocesses 306, 308 in the sequence on a wafer. Steps 408 to 418 aredescribed above in relation to FIG. 3.

The advantage of splitting the corrections between the scanner and theetcher is it gives more freedom. It is advantageous to compensate for acertain fingerprint at both the etch stage and at the preceding scannerstage. One could compensate on the etcher which is the last step butthen we know that some of these fingerprints cannot be compensated by anetcher. One should consider what can the etcher compensate and what cana scanner compensate. The scanner has most degrees of freedom. Forcertain fingerprints the etcher is better at compensating. Fortunately,it is also the etcher that may be causing the kind of fingerprint thatis to be corrected. If the fingerprint that the etcher is causing isknown then that can be compensated for that at the etcher and thefingerprint will tend to zero.

An example of actuating an etcher is by changing the temperature profilein the etch chuck. For CD, it is putting a temperature profile on thechuck. For overlay it is moving an outer ring up or down. Thatinfluences the direction of the electrical field at the edge of thewafer. Thus in effect the edge of the wafer is extended with a ring,which is also etched. The height of the ring can be adjusted to matchthe top of the wafer. By moving the ring up and down the overlay at theedge of the wafer is influenced.

Embodiments thus use both the scanner and etcher tools as actuators, andco-optimize their individual actuation efforts so as to minimize theafter-etch fingerprint without a need for specific wafer routing. E.g.the average etcher contribution may be taken into account in theactuation on the scanner. Should the etcher actuation be a limitingfactor due to constraints on how much the etch process can be changed,with the average etcher contribution taken care of on the scanner, theetcher would only have to correct for chamber dependent deltas withrespect to the average etch contribution.

Embodiments allow estimating deposition tool layer thickness variationson after etch CD without explicitly measuring layer thickness.

The granularity of the corrections can now be on wafer-level instead oflot-level.

Embodiments use context information from multiple fab processing toolslike etchers, CMP, RTA, resist spin and coat. The overlay fingerprintsgenerated by these tools on the resist layer can be accurately measuredper tool or tool-chamber that is causing the fingerprint.

Advantages of embodiments include giving higher yield, less metrologytime due to efficient aggregation of available information, moreefficient actuation, and no need for dedicated wafer routing.

A further advantage of the approach is that there is no need fordedicated wafer routing.

An embodiment of the invention may be implemented using a computerprogram containing one or more sequences of machine-readableinstructions describing methods of optimizing a sequence of processesfor manufacturing of product units, as described above. This computerprogram may be executed within a computing apparatus, such as controlunit LACU of FIG. 1, or some other controller. There may also beprovided a data storage medium (e.g., semiconductor memory, magnetic oroptical disk) having such a computer program stored therein.

Further embodiments of the disclosure are disclosed in the list ofnumbered clauses below:

-   1. A method for optimizing a sequence of processes for manufacturing    of product units, the method comprising:

(a) obtaining (408) a characteristic of a previous process in thesequence already performed on a product unit;

(b) obtaining (410) a characteristic of a subsequent process in thesequence to be performed on the product unit;

(c) determining (412), using the obtained characteristics, a predictedperformance parameter of the product unit associated with the sequenceof previous and subsequent processes; and

(d) determining (414) a first correction to a first future process inthe sequence to be performed on the product unit, based on thedetermined predicted performance parameter.

-   2. The method of clause 1, wherein the step (c) of determining a    predicted performance parameter comprises deriving a model from    statistical analysis of a plurality of measurement results of the    performance parameter for a plurality of characteristics of    processes in the sequence.-   3. The method of clause 1, wherein the step (c) of determining the    predicted performance parameter comprises the steps:

(c1) obtaining recorded (402) characteristics of processes in thesequence performed on a plurality of product units;

(c2) obtaining measurement results (404) of performance parameters foreach product unit out of the plurality of product units;

(c3) associating (406) the measurement results of the performanceparameters with the respective recorded characteristics; and

(c4) determining (412) a predicted performance parameter of the productunit associated with the sequence of previous and subsequent processesby using the obtained characteristics to retrieve measurement results ofthe performance parameters corresponding to the recordedcharacteristics.

-   4. The method of any preceding clause, wherein the characteristics    comprise context data representing one or more parameters of    processing of product units.-   5. The method of any preceding clause, wherein the performance    parameter comprises a fingerprint of variation across product units    of object data representing one or more parameters measured across    product units.-   6. The method of any preceding clause, further comprising the step    of applying the determined first correction to a process in the    sequence on a product unit.-   7. The method of any preceding clause, further comprising the step    of determining (416) a second correction to a second future process    in the sequence to be performed on the product unit, based on the    determined predicted performance parameter.-   8. The method of clause 7, further comprising the step of applying    the determined second correction to a process in the sequence on a    product unit.-   9. The method of clause 7 or clause 8, wherein the first correction    relates to variation across a plurality of tools of the determined    predicted performance parameter associated with the second future    process and the second correction relates to variation of a specific    tool.-   10. The method of any preceding clause, wherein a product unit is a    substrate.-   11. The method of any preceding clause, wherein the previous process    comprises a process on a product unit selected from the processes:    chemical mechanical polishing, deposition, thermal anneal, and    resist coat.-   12. The method of any preceding clause, wherein the first or second    future process comprises exposure of a product unit.-   13. The method of any preceding clause, wherein the first or second    future process comprises etch of a product unit.-   14. A computer program comprising computer readable instructions    which, when run on suitable computer apparatus, cause the computer    apparatus to perform the method of any of clauses 1 to 13.-   15. A computer program product comprising the computer program of    clause 14.

This control unit LACU may include a computer assembly as shown in FIG.5. The computer assembly may be a dedicated computer in the form of acontrol unit in embodiments of the apparatus according to the inventionor, alternatively, be a central computer controlling the lithographicapparatus. The computer assembly may be arranged for loading a computerprogram product comprising computer executable code. This may enable thecomputer assembly, when the computer program product is downloaded, tocontrol aforementioned uses of a lithographic apparatus with embodimentsof the level and alignment sensors AS, LS.

Memory 529 connected to processor 527 may comprise a number of memorycomponents like a hard disk 561, Read Only Memory (ROM) 562,Electrically Erasable Programmable Read Only Memory (EEPROM) 563 andRandom Access Memory (RAM) 564. Not all aforementioned memory componentsneed to be present. Furthermore, it is not essential that aforementionedmemory components are physically in close proximity to the processor 527or to each other. They may be located at a distance away.

The processor 527 may also be connected to some kind of user interface,for instance a keyboard 565 or a mouse 566. A touch screen, track ball,speech converter or other interfaces that are known to persons skilledin the art may also be used.

The processor 527 may be connected to a reading unit 567, which isarranged to read data, e.g. in the form of computer executable code,from and under some circumstances store data on a data carrier, like asolid-state drive 568 or a CDROM 569. Also DVD's or other data carriersknown to persons skilled in the art may be used.

The processor 527 may also be connected to a printer 570 to print outoutput data on paper as well as to a display 571, for instance a monitoror LCD (Liquid Crystal Display), of any other type of display known to aperson skilled in the art.

The processor 527 may be connected to a communications network 572, forinstance a public switched telephone network (PSTN), a local areanetwork (LAN), a wide area network (WAN) etc. by means oftransmitters/receivers 573 responsible for input/output (I/O). Theprocessor 527 may be arranged to communicate with other communicationsystems via the communications network 572. In an embodiment of theinvention external computers (not shown), for instance personalcomputers of operators, can log into the processor 527 via thecommunications network 572.

The processor 527 may be implemented as an independent system or as anumber of processing units that operate in parallel, wherein eachprocessing unit is arranged to execute sub-tasks of a larger program.The processing units may also be divided in one or more main processingunits with several sub-processing units. Some processing units of theprocessor 527 may even be located a distance away of the otherprocessing units and communicate via communications network 572.Connections between modules can be made wired or wireless.

The computer system can be any signal processing system with analogueand/or digital and/or software technology arranged to perform thefunctions discussed here.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description by example, and not oflimitation, such that the terminology or phraseology of the presentspecification is to be interpreted by the skilled artisan in light ofthe teachings and guidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

The invention claimed is:
 1. A method for configuring processing ofproduct units, the method comprising: obtaining a first characteristicof a first process, wherein the first process is used in processing oneor more product units and the first process comprises performing adeposition on the one or more product units, patterning of the one ormore product units using an exposure step and/or using a resistdevelopment process on the one or more product units; obtaining a secondcharacteristic of a second process, the second process to be used inprocessing the one or more product units; determining, by a hardwarecomputer system using the obtained first and second characteristics, aprediction of a performance parameter associated with the at least oneproduct unit of the one or more product units after being processedusing the second process; and determining a correction to a futureprocess to be used in processing the at least one product unit of theone or more product units based on the determined prediction.
 2. Themethod according to claim 1, wherein the first characteristic of thefirst process is an after development overlay fingerprint.
 3. The methodaccording to claim 1, wherein the second process is a process of etchingproduct units and the second characteristic of the second process iscontext data of an etcher to be used to etch the at least one productunit of the one or more product units.
 4. The method according to claim1, wherein the performance parameter is after etch overlay.
 5. Themethod according to claim 1, wherein the future process is a process ofpatterning product units using an exposure step and/or using a resistdevelopment process.
 6. The method according to claim 1, furthercomprising applying the correction to an apparatus to be used inperforming the future process.
 7. The method according to claim 1,wherein the determining of the predicted performance parameter is basedon using a model derived from analysis of a plurality of measurementresults of the performance parameter associated with a plurality ofproduct units and characteristics of the first and second process usedin processing the plurality of product units.
 8. The method according toclaim 1, further comprising obtaining the second characteristic of thesecond process used in processing the one or more product units.
 9. Themethod according to claim 8, wherein the determining of the predictedperformance parameter comprises deriving a model from analysis of aplurality of measurement results of the performance parametercorresponding to a plurality of second characteristics of the secondprocess.
 10. A computer program product comprising a non-transitorycomputer-readable medium having computer readable instructions therein,the instructions, when executed by a computer system, configured tocause the computer system to at least: obtain a first characteristic ofa first process, wherein the first process is used in processing one ormore product units and the first process comprises performing adeposition on the one or more product units, patterning of the one ormore product units using an exposure step and/or using a resistdevelopment process on the one or more product units; obtain a secondcharacteristic of a second process, the second process to be used inprocessing the one or more product units; determine, using the obtainedfirst and second characteristic, a prediction of a performance parameterassociated with the at least one product unit of the one or more productunits after being processed using the second process; and determine acorrection to a future process to be used in processing the at least oneproduct unit of the one or more product units based on the determinedprediction.
 11. The computer program product according to claim 10,wherein the first characteristic of the first process is an afterdevelopment overlay fingerprint.
 12. The computer program productaccording to claim 10, wherein the second process is a process ofetching product units and the second characteristic of the secondprocess is context data of an etcher to be used to etch the at least oneproduct unit of the one or more product units.
 13. The computer programproduct according to claim 10, wherein the performance parameter isafter etch overlay.
 14. The computer program product according to claim10, wherein the future process is a process of patterning product unitsusing an exposure step and/or using a resist development process. 15.The computer program product according to claim 10, wherein theinstructions are further configured to cause the computer system tocause application of the correction to an apparatus to be used inperforming the future process.
 16. The computer program productaccording to claim 10, wherein the instructions are further configuredto cause the computer system to obtain the second characteristic of thesecond process used in processing the one or more product units.
 17. Thecomputer program product according to claim 10, wherein the instructionsconfigured to cause the computer system to determine the predictedperformance parameter are further configured to cause the computersystem to derive a model from analysis of a plurality of measurementresults of the performance parameter corresponding to a plurality ofsecond characteristics of the second process.
 18. The computer programproduct according to claim 10, wherein the instructions configured tocause the computer system to determine the predicted performanceparameter are further configured to cause the computer system todetermine the predicted performance parameter based on using a modelderived from analysis of a plurality of measurement results of theperformance parameter associated with a plurality of product units andcharacteristics of the first and second process used in processing theplurality of product units.
 19. A computer program product comprising anon-transitory computer-readable medium having computer readableinstructions therein, the instructions, when executed by a computersystem, configured to cause the computer system to at least: obtain afirst characteristic of a first process, wherein the first process isused in processing one or more product units; obtain a secondcharacteristic of a second process, the second process to be used inprocessing the one or more product units; determine, using the obtainedfirst and second characteristic and using a model, a prediction of aperformance parameter associated with the at least one product unit ofthe one or more product units after being processed using the secondprocess, the model derived from analysis of a plurality of measurementresults of the performance parameter associated with a plurality ofproduct units and characteristics of the first and second process usedin processing the plurality of product units; and determine a correctionto a future process to be used in processing the at least one productunit of the one or more product units based on the determinedprediction.
 20. The computer program product according to claim 19,wherein the future process is a process of patterning product unitsusing an exposure step and/or using a resist development process.